19980618014379A

(.4)During preflight weather briefing, the pilot was briefed to expect rain showers and thunderstorms up to level 6 (extreme) intensity along his route of flight. The pilot, whose aircraft was equipped with radar and stormscope equipment, filed an instrument flight rules (IFR) flight plan and departed under IFR. Upon radar contact, ATC cleared the pilot direct to his destination. 21 minutes later, while flying on the direct (northwesterly) track to the destination, the aircraft entered a level 4 thunderstorm cell. The pilot told air traffic control (ATC), '...[I] hit a pretty heavy cell here [I've] got lightning all around and picking up some hard ice.' The crew of another aircraft deviating to the north of the storm suggested the aircraft turn north to exit the weather. ATC relayed this suggestion, and the pilot replied he was turning to the north. The aircraft then entered a right turn; radar contact was lost after approximately 90 degrees of turn. 6 seconds after the time at the last radar position, the pilot radioed, '...[I'm] in a tremendous downdraft [I'm] losing altitude six thousand'. This was the last transmission received from the accident aircraft. A search for the aircraft was initiated, the aircraft wreckage was found approximately 11 1/2 hours later, approximately 1 1/2 miles south of the last radar position. Logbooks recovered from the wreckage indicated the pilot was not current for IFR flight. (-23)aircraft encountered thunderstorm during enroute phase of flight. Pilot reported 6,000 ft/min downdraft and couldn't maintain altitude. Pilot also reported picking up ice. Assigned enroute altitude was at 16,000 ft; crash site elevation 5600 ft. great falls afss weather briefing at 06190251 states that doppler radar levels reaching 57, level 6 and above in intensity, extreme along flight route.